I cant imagine using ordinary white glue (PVA glue) at all, on metal cameras, its a very common wood glue and excellent for that, also for paper and cloth, i think it is used in bookbinding as well. it would soak in and adhere to the leather but not the metal..not sure i would want it soaking in to the leather on the camera anyway.
personaly i would never use contact cement either, its just not needed and overkill, messy to clean up (and dont kid yourself, most people will get some on parts of the camera they didnt intend on, so you may always see little bits of it) and good luck removing the leather if you need to once its set.
shellac is ideal, easy to use, authentic for old cameras, its what they used in the early days and can be removed easily and cleans up ok.
i also like the rubber cement and often use it (same stuff as used for repairing punctures in tire tubes and adhering rubber soles on shoes, although some people may use contact glue for shoes as well) , for small patch jobs, such as if the corners are curling up, providing i am not being criticle about keeping the camera genuine, though it would be fine for whole camera leather replacment as well...
its easy and a good choice when you want something straight out of a tube, the leather can be moved around a bit to get it in the right place, if you muck it up altogether it can be fixed, obviously it can be removed. clean up if gotten on other parts is easy and dries pretty much clear.